FIELD OF THE INVENTION
The present invention relates to a rotor for a shortcircuited alternating current motor, and having a pack of circular rotor blades fixedly mounted on a shaft, the plates have, uniformly around the peripheral edges thereof, a number of recesses which, when the plates are packed, form generally axially extending rotor slots, and each rotor slot includes a first recess or cavity whose peripheral edge forms a closed contour and which accommodates a conductor radially inwards of the mantle surface of the rotor, the peripheral edge of said first recess has a concavity which faces towards said peripheral edge, and a second recess which forms a radially extending slot which extends from a point close to the concavity and out towards said peripheral edge, and a bridge is formed between the first recess and the second recess.
A rotor of this kind is known from U.S. Pat. No. 5,155,404. This known construction is intended for variable frequency operation, wherein the said first recesses are filled with conductors, whereas the second recesses form air gaps. The surfaces between the recesses form an iron bridge to which the major part of the circumferential magnetic leakage field passes, and where damping of the harmonic overtones from the current source can be achieved and the losses generated by said overtones therewith decreased, as a result of saturation effects.
It has long been known to provide short-circuited AC-motors with double rotor slots, in the form of so-called double squirrel-cage rotors. This affords an improved torque curve at high starting torques and the starting current is also slightly lower than in the case of normal so-called single squirrel-cage rotors.